1. Field of the Invention
This invention relates to a flash-back arrestor set in a valve body in a dissolved acetylene cylinder.
2. Description of the Prior Art
Acetylene is extremely unstable and liable to be decomposed and exploded. Therefore, acetylene is currently used for industrial purposes (welding and cutting) in the form of "dissolved acetylene", in which acetylene is stabilized with a solvent (acetone or dimethylformamide (DMF)) and a porous filling material called "mass" (calcium silicate, charcoal, or a charcoal-asbestos mixture). The General High-pressure Gas Security Rules stipulate that acetylene shall be charged into a cylinder provided therein with a porous filling material which is wetted with acetone or DMF and which has passed a porous material performance test conducted by the High-pressure Gas Security Association.
There is much room for further improvement with respect to the security of an existing dissolved acetylene cylinder. The most important problem resides in that an existing cylinder of this kind has an insufficient flash-back preventive performance. Acetylene often causes fire and explosion while it is being charged into an acetylene cylinder, and flash-back while it is being consumed in a welding or cutting operation. Under the following conditions, a safety plug provided in a dissolved acetylene cylinder may be actuated due to flash-back to result in the ejection of gas or the explosion of the cylinder.
(1) The amount of acetylene in the cylinder is unduly large. PA1 (2) The temperature of the cylinder is high. PA1 (3) The temperature of actuation of a safety plug, which consists of a fusible alloy, is excessively low. PA1 (4) Air is accumulated as an impurity gas in the cylinder.
A longitudinal section of an example of a conventional dissolved acetylene cylinder is shown in FIG. 1. Referring to FIG. 1, a porous material 2 consisting of mainly calcium silicate is provided in a cylinder 1, and the porous material 2 is wetted with a solvent (acetone or DMF). Felt or animal hair 5 is packed in a recess 4 formed in that portion of the porous material 2 which is just under a valve 3 for the container 1. The felt or animal hair 5 functions mainly as a filter. When flash-back into the container 1 occurs under the above-mentioned conditions, the felt is carbonized, and the decomposition thereof progresses to cause a safety plug 6 to be actuated. This often results in the ejection of gas or the explosion of the cylinder.
Some of the accidents of flash-back into an acetylene cylinder, that have occurred lately are ascribed to the adiabatic compression of the air at the acetylene cylinder side of the interior of a pressure regulator. A flash-back arrestor now on the market is so designed that it is set at a low pressure side of a pressure regulator (at such side of a pressure regulator that is away from the acetylene cylinder). Therefore, the flash-back arrestor has no effect on the prevention of the flash-back referred to above. Furthermore, it is impossible that such a commercially available flash-back arrestor be set in each acetylene cylinder when a number of acetylene cylinders are joined together to charge them with acetylene gas in an acetylene charging factory, or when a manifold is used to discharge the acetylene gas.